Liquid-solid separator

ABSTRACT

A batch centrifuge for separation of minute solid particles suspended in a liquid fraction comprises a bowl having a cover and a shell both mounted on a vertical drive shaft. The shell is moved upwardly to closed position in response to admission of a control liquid between its underside and a bottom on the shaft. The settling space of the bowl is surrounded by a ring-shaped clearance defined by the cover and shell inwardly of two ringshaped end faces which sealingly engage each other in closed position of the shell. A sealing ring seals the clearance on admission of control liquid into an annular compartment of the shell, and the latter further supports a control valve which normally seals an outflow passage for rapid evacuation of liquid fraction when the outermost part of the settling space accumulates a cake of solid particles. The remaining liquid fraction is expelled from the cake by way of the clearance in response to retraction of the sealing ring, and the cake is caused to disintegrate and is expelled radially outwardly upon movement of the shell away from the cover.

United States Patent Pause 5] Mar. 14, 197 2 [5 LIQUID-SOLID SEPARATOR 3,415,446 12/1968 Weiland ..233/ R [72] Inventor: Kurt Pause, Grevenbroich, Germany Primary Examiner jordan Franklin [73] Assignee: Maschineniabrik Buckau R. Wolf Aktien- Assistant Examiner-George H. Krizmanich gesellschaft, Grevenbroich, Germany Attorney-Michael S. Striker [22] Filed: July 14, 1969 [57] ABSTRACT [21] APPLNO: L290 A batch centrifuge for separation of minute solid particles suspended in a liquid fraction comprises a bowl having a cover Foreign Application Priority Data and a shell both mounted on. a vertical drive shaft. The shell is moved upwardly to closed position in response to admission of NOV. 29, Germany ..P a control between underside and a on the shaft. The settling space of the bowl is surrounded by a ring- [52] U.S.Cl ..233/20 shaped clearance defined by the cover and she inwardly of [51] Int. Cl ..B04b 11/00 [58] Field MS I 233/20 20 A l 1 A 19 two ring-shaped end faces which sealingly engage each other 5 in closed position of the shell. A sealing ring seals the clearance on admission of control liquid into an annular compartment of the shell, and the latter further supports a control [56] References Cited valve which normally seals an outflow passage for rapid UNITED STATES PATENTS evacuation of liquid fraction when the outermost part of the settling space accumulates a cake of sohd particles. The A remaining fraction is expelled from the cake way of 2,840,302 6/1958 Semacker at 233/20 A the clearance in response to retraction of the sealing ring, and 2,955,754 10/196o Y P R the cake is caused to disintegrate and is expelled radially outggggi i a wardly upon movement of the shell away from the cover. ys o ov 3,409,214 11/1968 Thylefors ..233/20 R 35 Claims, 9 Drawing Figures r" 2a50 66 2/ a 9 57 44 68 42 52 I8 V 57 L3 B2 4 L PATENTEDMAR 14 I972 33. 648 926 SHEET 1 OF 4 FIG] a 59 IN VENTOR I K urf PAUSE his A TTORNEY PATENTEDMAR 14 I972 3. 648 926 sumanra FIG. 2 v 6 \/67 66 v\ i w a 4 -INVEN TOR:

Kurt PAUSE his ATTORNEY PATENTEDMAR 14 1972 3.648 926 sum 3 [1F 4 IN VEN TOR: Kurt PAUSE his ATTORNEY LIQUID-SOLID SEPARATOR BACKGROUND OF THE INVENTION The present invention relates to liquid-solid separators in general, and more particularly to improvements in centrifuges. Still more particularly, the invention relates to improvements in so-called batch centrifuges wherein successive batches of a suspension are treated to segregate solid particles from the liquid fraction.

It is already known to employ batch centrifuges for separation of solid particles from the liquid fraction of a suspension, eg, in galvano-electrolytic metalplating and electro-chemical metalworking techniques leading to precipitation of extremely fine slurries. If the size of solid particles is very small, the centrifuge preferably comprises an open-and-shut bowl which is driven at a constant speed. A complete working cycle involves the admission of a batch of suspension into the bowl, expulsion of the liquid fraction and evacuation of solid residue from the bowl. Since the concentration of solid particles in the suspension normally fluctuates, the interval which is required for accummulating a predetermined amount of solid particles in the bowl varies within a rather wide range. The remaining stages of a cycle (i.e., opening the bowl, evacuating the solid particles, and closing the bowl) require fixed intervals of time and can be regulated in accordance with a predetermined schedule. Thus, the operation of a conventional batch centrifuge can be controlled by a programming unit with the exception of terminating the admission of suspension (when the closed bowl completes the accumulation of a predetermined quantity of solid particles).

In accordance with a presently known proposal, the openand-shut bowl is held in closed position under the pressure of the liquid fraction which is separated from solid particles in the interior of the bowl. Once the bowl has accumulated a certain quantity of solid particles, a small gap is opened in the radially outermost region of the settling space in the bowl so that the liquid which is still entrapped in the settled solid material can escape from the bowl prior to evacuation of solids. This is the filtering stage of the cycle. The bowl is then caused to open fully and the solids are evacuated into the same chamber which was used for collection of liquid fraction during the preceding (filtering) stage. Such types of centrifuges can be used with advantage for separation of small electrically neutral crystalline and/or amorphous particles.

A drawback of the just described centrifuge is that the closing pressure of separated liquid does not exceed the pressure of liquid in the settling space. Furthermore, when a cycle is started, the closing pressure is zero so that a substantial amount of suspension escapes prior to complete filling of the settling space. Once the settling space is filled, the liquid produces a pressure which causes the bowl to close so that the settling process begins. Certain centrifuges are designed to operate with a supply of separated (clarified) liquid fraction so that the bowl can be closed immediately and the admission of suspension begins only after the bowl is closed. This necessitates the retention of a supply of clarified liquid fraction and unduly prolongs the cycle because the suspension is admitted with a certain delay, i.e., subsequent to closing of the bowl.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel and improved batch centrifuge for separation of solid particles which are suspended in a liquid fraction, and to construct and assemble the centrifuge in such a way that the admission of a fresh batch of suspension into the bowl can take place practically simultaneously with completion of evacuation of solid particles which are separated from the previously admitted batch.

Another object of the invention is to provide a novel system for closing and opening the open-and-shut bowl of a batch centrifuge and to provide such centrifuge with novel means for initiating the filtration of solid particles in the settling space of the bowl.

A further object of the invention is to provide a novel sealing system for the open-and-shut bowl of a batch centrifuge.

An additional object of the invention is to provide a batch centrifuge wherein the accumulated solid particles can be evacuated from the bowl in a novel and time saving way.

The invention is embodied in a centrifuge for treatment of suspensions of minute solid particles in a liquid fraction. The centrifuge comprises a substantially vertical drive shaft, an open-and-shut bowl driven by the shaft and including a first portion or cover and a second portion or shell movable axially of the shaft to and from a closed position in which the two portions define an annular settling space the radially outermost part of which serves to accumulate solid particles, a narrow clearance defined by the two portions of the bowl radially outwardly of the outermost part of the settling space, first sealing means mounted in the bowl (preferably in the second portion) adjacent to the clearance, hydraulic operating means (including a supply of control liquid) for effecting movements of the sealing means between sealing and open positions to thereby respectively prevent and permit escape of the liquid fraction by way of the clearance, feeding means for supplying batches of suspension into the settling space in sealing position of the first sealing means so that the solid particles accumulate in the outermost part of the settling space and form therein a cake containing some of the liquid fraction which is automatically expelled by centrifugal force through the clearance in open position of the first sealing means, and second sealing means provided between ring-shaped sealing faces of the first and second portions of the bowl radially outwardly of the clearance. The minimum width of the clearance preferably equals the average size of solid particles in the suspension which latter is preferably admitted by way of the upper end portion of the shaft. The control liquid is preferably admitted to the bowl through passages provided therefor in the lower end portion of the shaft.

When the second portion is moved downwardly and away from the first portion of the bowl, the two portions define a relatively wide ring-shaped discharge. opening which extends between the end faces of the two portions and permits rapid evacuation of the cake from the outermost part of the settling space. Such cake is caused to disintegrate in response to tangential forces which develop on rotation of the bowl, and the resulting minute fragments are intercepted in a collecting chamber provided in a stationary housing of the centrifuge radially outwardly of the discharge opening. When the outermost part of the settling space is filled with solid particles, the remaining suspension is permitted to rapidly escape from the settling space by way of an outfiow passage which is preferably provided in the second portion of the bowl radially inwardly of the outermost part and is normally sealed by a control valve which is held in sealing position by control liquid admitted by the operating means through passages provided in the shaft and channels in the second portion of the bowl.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved centrifuge itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of a centrifuge which embodies one form of the invention, the left-hand portion of the bowl being shown in closed position and the right-hand portion of the bowl being shown in open position;

FIG. 2 is an enlarged fragmentary axial sectional view of the bowl in closed position;

FIG. 3 is an enlarged fragmentary axial sectional view of the bowl in open position;

FIG. 3a is an enlarged view of a detail which is encircled in FIG. 3;

FIG. 4 is an enlarged horizontal sectional view as seen in the direction of arrows from the line IV-IV of FIG. 1;

FIG. is an enlarged vertical sectional view as seen in the direction of arrows from the line VV of FIG. 1;

FIG. 6 is a fragmentary axial sectional view of a second centrifuge, with the first sealing means shown in sealing position;

FIG. 7 illustrates the structure of FIG. 6 but with the first sealing means shown in open position; and

FIG. 8 is a fragmentary axial sectional view of a third centrifuge, with the first sealing means shown in sealing position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 to 3, there is shown a liquid-solid separator in the form of a batch centrifuge which comprises a housing or main support 1 accommodating a vertical drive shaft 2 the upper end portion of which is rotatably mounted in a swivel bearing 3 so that it cannot move axially. An auxiliary bearing 4 is provided in a tubular portion la of the housing 1 to surround the lower end portion of the drive shaft 2. This auxiliary bearing 4 is surrounded by an elastic ring 5 which transmits radial stresses to the tubular housing portion 1a. The ring 5 preferably consists of a material which does not produce any appreciable clamping action; this eliminates undesirable effects of the forces which oppose the spinning action. Thus, the bowl which is carried by the shaft 2 can change its position in response to minor imbalance to automatically compensate for unequal distribution of masses.

The bowl of the centrifuge comprises a conical upper portion or cover 6 which is rigidly secured to the drive shaft 2. A second bowl portion or shell 8 is axially movably mounted on the drive shaft 2 at a level below the cover 6 in such a way that it shares all angular movements of the cover. The left-hand portion of FIG. 1 illustrates the shell 8 in its upper end position or closed position and the right-hand portion of FIG. 1 shows the shell 8 in its lower end position or open position. The closed and open positions of the shell 8 are respectively shown on a larger scale in FIGS. 2 and 3. FIG. 2 further shows a portion of a system of radial channels 23 for evacuation of the liquid fraction, and FIG. 3 shows channels 36, 38, 39, 40 and 41 whose function is to supply to the bowl a control liquid.

A third combination portion or bottom 11 is fixedly mounted on the shaft 2 at a level below the shell 8. This bottom 11 has a circumferential groove for a multi-section piston ring 12 which engages the shell 8. In the illustrated embodiment, the piston ring 12 comprises two semicircular sections which define two gaps located diametrically opposite each other to permit a certain amount of leakage for reasons which will be fully explained hereinbelow. As stated above, the three portions 6, 8 and 11 of the bowl share all angular movements of the drive shaft 2; they are preferably driven at a constant speed. The operation of the centrifuge can be described as a periodic-automatic operation.

The cover 6 has an annular lower end face 7 (FIG. 3) which is adjacent to its circumference and registers with an annular upper end face of the shell 8. When the shell 8 is caused to assume its closed position (best shown in FIG. 2), the annular end faces 7, l0 prevent escape of any material due to the provision of a novel sealing device which will be described later. The shell 8 then defines with the cover 6 a sealed ringshaped settling space 9 whose radially outermost part serves to collect solid particles irrespective of the size of such particles.

It is desirable to abruptly accelerate the'suspension in the settling space 9 to the exact speed of the drive shaft 2. This is achieved by the provision of a large number of radially extending closely adjacent vanes 13 which extend into the settling space 9 and are integral with or secured to the shell 8. For example, and as shown schematically in FIG. 4, the angular distance between adjoining vanes 13 need not exceed 2 to 3, i.e., the shell 8 can carry as many as I80 vanes or even more. The shell 8 further carries a ring-shaped control valve assembly including a piston 14 which is movable in the axial direction of the drive shaft 2 and is installed between a readily deformable soft gasket 18 and a deformable ring 19. The parts 18, 19 can consist of rubber and may be vulcanized into the shell 8. At least the ring 19 tends to retract the piston 14 into a groove 15 of the shell 8.

When the operation of the centrifuge is started, the settling space 9 is practically empty so that its radially outermost part can collect solid particles which accumulate therein subsequent to travel radially outwardly under the action of centrifugal force. As the solid particles continue to accumulate in the settling space 9, the effective depth of the outermost part of this space decreases and there develops a turbulent zone in the region between the cake of deposited solid particles and an overflow channel 22 (see FIGS. 1 and 3). Thus, the separation of solid and liquid fractions becomes less effective or ceases to proceed at all even though the settling space 9 is not filled with solid particles all the way to the overflow channel 22. If the admission of suspension were to be interrupted at such stage of operation (i.e., subsequent to formation of the aforementioned turbulence zone), the suspension could quiet down and the solid particles could become separated from the liquid. However, this would mean that a relatively deep layer of liquid would accumulate radially inwardly of the cake of solid particles in the settling space 9 and that such liquid could not escape by way of the overflow channel 22 because the latters inlet would be blocked by solids. All such liquid would have to escape by way of a relatively narrow clearance 60 provided between the shell 8 and cover 6 inwardly of the end faces 7, 10 and surrounding the outermost part of the settling space 9 (see FIG. 2). Furthermore, the liquid fractions which would escape by way of the clearance 60 would have to penetrate through the cake of solid particles in the outermost part of the settling space 9. This would unduly prolong the time necessary for evacuation of the liquid fraction, i.e., the operation of the centrifuge would be rather uneconomical because the evacuation of liquid fraction from the settling space 9 would consume an amount of time whose length is unwarranted in comparison with the time required to complete the treatment of a batch of suspension. The function of the aforementioned piston 14 is to effect rapid evacuation of such liquid fraction which is located at the lower level of the turbulence zone in the settling space 9, and the piston 14 is opened when necessary to permit rapid evacuation of liquid prior to filtering and prior to expulsion of caked solid particles. When moved to open position, the piston 14 exposes an annular outflow passage 44 through which the liquid can rapidly escape into the system of radial channels 23. The escaping liquid entrains a portion of the cake from the settling space 9; this is desirable because it insures that only the properly settled solid particles remain in the settling space subsequent to opening of the piston 14 and in response to resulting rapid evacuation of the liquid fraction. Thus, once the piston 14 permits the liquid to escape, the settling space 9 contains only such liquid which is entrapped in the cake of settled solid particles. Consequently, time required for expulsion of such liquid from the cake of particles in the settling space 9 (filtering step) is reduced accordingly.

The control valve assembly including the parts l4, l8 and 19 is mounted in the ring-shaped groove 15 and forms with the shell 8 one but preferably two or more control chambers 17. FIG. 2 shows that the valve assembly forms with the shell 8 two control chambers 17 which are located below the gasket 18 and ring 19. The extent of axial (upward) movement of the piston 14 is limited by a stop 16 which is an internal surface provided on the shell 8 at a level above a portion of the supper surface of the control valve (see FIG. 3). The piston 14 has an upper surface which is flush with the adjoining surface of the shell 8 (see FIG. 2) in closed or sealing position of the control valve assembly. When the control liquid which normally fills the control chambers 17 is permitted to escape, the ring 19 and/or the gasket 18 retracts the piston 14 into the groove 15.

The feeding means for supplying suspension into the bowl comprises a fixedly mounted pipe 20 (FIG. 1) which is secured to the housing 1 and projects into a downwardly diverging axially extending blind bore 2a machined into the upper end portion of the drive shaft 2. The latter is further provided with ports or ducts 21 which convey the suspension from the lower portion of the blind bore 2a whereby such suspension flows toward the settling space 9. The position of ports 21 with reference to the axis of the drive shaft 2 is best shown in FIG. 4. It will be noted that the ports 21 extend substantially tangentially of the adjoining portion of the blind bore 2a, i.e., that they are not exactly radial to the axis of the drive shaft. Their outer ends direct the suspension backwards, as considered in the direction of rotation of the drive shaft 2, in order not to accelerate the suspension during entry into the bowl.

When the ports 21 admit suspension, the settling space 9 is being filled with solid particles in a direction from its radially outermost part toward the axis of the drive shaft 2, i.e., toward the overflow channel 22. If the suspension is admitted continuously, the bowl discharges the same amount of suspension as the amount admitted by the ports 21 as soon as the settling space 9 is filled. The overflowing liquid leaves the settling space 9 by way of the overflow channel 22 and the aforementioned system of radial channels 23 which discharge tangentially into an intercepting compartment 24 provided in the housing 1.

A pump 25 which forms part of a hydraulic operating unit is installed in the lower portion of the housing 1 to circulate a control liquid substantially without pressurization through conduits 26, 28, 30. The conduits 28 and 30 respectively contain flow regulating valves 27 and 29. The lower portion of the drive shaft 2 is formed with an elongated axial blind bore 32 which accommodates a tube 31 so that the bore 32 is divided into an inner passage 34 (i.e., the internal space of the tube 31) and an outer passage 33 (the annular clearance between the tube 31 and the cylindrical internal surface of the drive shaft 2). The conduits 28, 30 respectively communicate with the passages 33 and 34. The upper end of the outer passage 33 communicates with liquid distributing bores or passages 35 extending radially of the drive shaft 2 and serving to deliver control liquid into a cylinder chamber 11A between the bottom 11 and the underside of the shell 8. The cylinder chamber 11A communicates with an overflow bore 46 of the bottom 11. The upper end of the inner passage 34 communicates with radially extending distributing bores or passages 37 provided in the drive shaft 2 to supply control liquid to the control chambers 17 below the gasket 18 and ring 19. The bores 37 further supply control liquid to an annular compartment 43 below a sealing ring 42 which is mounted in the shell 8 inwardly of the end face (see FIG. 3). When the chambers 17 receive control liquid, the piston 14 cooperates with the shell 8 to deform the gasket 18 and to thereby seal the outflow passage 44 of the shell (see FIG. 2). As best shown in FIG. 3, the shell 8 defines with the drive shaft 2 a ring-shaped liquid intercepting chamber 83 which is located at the level of the distributing bores 37 and communicates with one, two or more channels 41 of the shell 8. The channel 36 branches from the channel 41 to deliver control liquid to the compartment 43 below the sealing ring 42. The channels 39 and 40 connect the channel 41 with the control chambers 17 below the gasket 18 and ring 19. The compartment 43 is in communication with the channel 38 which discharges control liquid by way of flow restricting orifices 45 (see FIG. 3a).

The shell 8 and bottom 11 are respectively provided with radially extending projections or ribs 47, 48 (see FIG. 5) which define a set of radially extending channels 49 wherein the control liquid undergoes acceleration to circulate at the speed of the drive shaft 2. This insures that the control liquid can rapidly furnish a pressure which is needed to move the shell 8 from its open to its closed position.

Referring again to FIG. 1, the housing 1 defines a ringshaped space 50 which is adjacent to the cover 6 and is provided with tangential inlets (not shown) for admission of air or protective gas. The thus admitted gaseous fluid is accelerated in response to friction with the adjoining external surface 51 of the cover 6 and the accelerated fluid serves to expel crumblike particles from a collecting chamber 52 which communicates with the space and is outwardly adjacent to the end faces 7 and'10. The collecting chamber 52 is provided with tangential outlets (not shown) for the gaseous fluid.

The control liquid which is admitted into the drive shaft 2 by way of the passages 33, 34 is caused to accumulate in a reservoir or tank 55 which constitutes a source of control liquid and receives such liquid by way of a passage defined by annular guide members or baffles 53, 54 respectively mounted on the bottom 11 and shell 8. The outlet 56 of the tank 55 is connected with the conduit 26 which supplies control liquid to the suction side of the pump 25. The arrows applied to the lines representing the conduits 26, 38, 30 indicate the direction of liquid flow therein.

In order to insure that the liquid fraction which is entrapped in the caked solid particles contained in the outermost part of the settling space 9 can escape by way of the narrow clearance without entraining an unduly large quantity of solid particles, the width of the clearance 60 must be extremely small, preferably in the range of 0.001 millimeter. This is desirably because the outflowing liquid could entrain the smallest solid particles during flow through the clearance 60. This clearance is located radially inwardly of the metallic end faces 7, 10 of the cover 6 and shell 8. These end faces must be free to move very close to each other to insure a practically complete surface-to-surface abutment between the parts 6 and 8. The narrow clearance 60 must'be completely sealed (by ring 42) during sedimentation of solid particles in the outermost part of the settling space 9. Since it is very difficult to insure satisfactory sealing action between relatively large metallic surfaces, there is provided a novel and improved sealing device which insures absolutely tight sealing action between the end faces 7 and 10 when the shell 8 dwells in its closed position. Such sealing device is outwardly adjacent to the clearance 60 and comprises a sealing ring 57 which is recessed into the end face 10 of the shell 8 and can bear against the end face 7 of the cover 6 when the shell assumes its closed position. The sealing ring 57 preferably consists of an incompressible material, such as synthetic rubber, polyurethane, soft polyvinyl chloride, Teflon (trademark) or the like. It is also possible to employ other soft synthetic thermoplastic materials or natural rubber. In order to ensure that the upper surface of the sealing ring 57 moves into requisite sealing engagement with the end face 7 of the cover 6 when the shell 8 moves toward and dwells in the closed position shown in FIG. 2, the end face 7 is preferably provided with an annular protuberance or ridge 64 (see FIG. 3) which penetrates into the central part of the upper surface of the ring 57 and deforms the latter so that the material of the ring 57 spills into two annular grooves (FIG. 3) which flank the ridge 64. The provision of grooves 65 is necessary because the material of the sealing ring 57 is preferably incompressible. The thus deformed ring 57 establishes with the end face 7 of the cover 6 an absolutely fluidtight seal which prevents escape of solid particles from the settling space 9 and radially beyond the clearance 60. The just described sealing device including the ring 57, the ridge 64 and grooves 65 of the cover 6 can be utilized in many other types of centrifuges and elsewhere where a fluidtight seal is to be established between two closely adjacent surfaces. As clearly shown in FIG. 1, the sealing ring 57 is installed downstream of the sealing ring 42, as considered in the direction of liquid flow from the settling space 9. A connecting bore 69 is provided in the shell 8 between the radially outermost portion of the clearance 60 and the radial channels 23.

When the shell 8 is moved to the open position of FIG. 3, the end faces 7 and 10 define a relatively wide annular discharge opening 61-which is located at a level above the plane 62 of the uppermost portion of the shell 8 outwardly of the settling space 9. The line 63 denotes in FIG. 3 the plane of the lowermost portion of the cover 6, such lowermost portion being an annular ridge located inwardly of the end face 7. It will be noted that the planes 62 and 63 are selected in such a way that the escaping solid particles cannot touch the sealing ring 57 and/or the ridge 64. This is desirable because the erosive action of certain types of solid particles could cause excessive wear and/or other damage to parts 57, 64 and would thus prevent proper sealing action between the cover 6 and shell 8.

FIG. 1 shows that the shaft 2 defines with the cover 6 a ringshaped distributor chamber 66 which receives suspension from the ports 21 of the shaft 2 and is bounded by smooth surfaces. The distributor chamber 66 forms part of a feeding passage through which the suspension flows on its way into the settling space 9. A portion of this feeding passage is bounded from below by a flange 68 which forms part of the shell 8 and defines with the adjacent portion of the cover 6 a narrow annular gap 67 serving to establish communication between the distributor chamber 66 and the settling space 9. The purpose of the gap 67 is to effect substantial acceleration of the suspension prior to entry into the space 9, Le, before the suspension impinges against the orbiting vanes 13 of the shell 8. The flange 68 overlies the inner portions of the vanes 13, namely, such portions which are nearer to the drive shaft 2.

The means for rotating the shaft 2 comprises a pulley 58 which is preferably integral with the upper end portion of the drive shaft and is rotated by an endless belt 59 or the like. The prime mover (e.g., an electric motor), the transmission and the certain other components of the means for rotating the shaft 2 are of conventional design.

The operation is as follows:

In the first step, the motor which drives the belt 59 is started to rotate the drive shaft 2 and the parts 6, 8, ll ofthe bowl at a predetermined speed. The motor of the pump 25 is also started and the flow regulating valve 27 is opened to admit control liquid into the outer passage 33, bores 35 and cylinder chamber 11A. The aforementioned radially extending channels 49 (FIG. between the ribs 47, 48 form part of the cylinder chamber 11A. Some liquid is free to escape through the gaps defined by the arcuate portions of the piston ring 12 and to descend onto the baffle 53 which cooperates with the baffle 54 to direct such control liquid into the tank 55. The passage 33 delivers control liquid to the chamber 1 1A at a rate which exceeds the rate ofleakage between the portions of the piston ring 12 so that the volume of the chamber 11A increases and the liquid causes the shell 8 to move from the open position of FIG. 3 to the closed position shown in FIG. 2. Additional surplus control liquid can escape from the chamber 11A by way of the overflow bore or bores 46 to descend onto the baffle 53 which returns such liquid into the tank 55. The liquid which fills the chamber 11A and circulates by centrifugal force exerts on the shell 8 a predetermined pressure which suffices to insure satisfactory sealing action between the ring 57 and the end face 7, i.e., between the shell 8 and cover 6 ofthe bowl.

The flow regulating valve 29 in the conduit 30 is also opened so that the pump 25 can supply control liquid into the passage 34 and bores 37 of the drive shaft 2. The bores 37 admit control liquid into the channel 41 of the shell 8 and the channel 41 admits liquid to the channel 36, i.e., to the annular compartment 43 below the sealing ring 42. The channels 39, 40 also receive liquid from the channel 41 and supply such liquid to the control chambers 17 below the gasket 18 and ring 19. When the annular compartment 43 receives liquid, the sealing ring 42 undergoes deformation to assume the shape shown in FIG. 2 and to thereby completely seal the gap 60 from the settling space 9. The pressure of control liquid continues to rise and propagates itself into the control chambers 17 to act on the piston 14 until the piston reaches the stop 16 of the shell 8. The liquid deforms the gasket 18 and the ring 19 whereby the latter expands into the settling space 9. Deformation of the gasket 18 results in sealing of the outflow passage 44. Thus, the settling space 9 is completely sealed save for the overflow channel 22. The conduit 30 admits to the inner passage 34 control liquid at a rate which exceeds the rate of liquid outflow so that some (but not all of) the surplus flows through the flow restricting orifices 45 (FIG. 3a). The

remainder of the surplus liquid leaves the channels 41 at 82 (FIG. 3) and enters the chamber 11A (and its channels 49) by way of the ring-shaped intercepting chamber 83. The just described liquid circulating system insures the application of constant pressure to all of the gaskets and sealing rings.

The suspension is thereupon admitted by way of the feeding pipe 20. Such suspension flows through the ports 21 and the distributor chamber 66 which rotates at a speed exceeding the rotational speed of the suspension. Thus, the suspension slides along the adjoining surfaces. Since the surface surrounding the outer side of the chamber 66 is only slightly conical, the suspension in the chamber 66 is subjected to a relatively small axial force, i.e., the force which tends to move the suspension toward the gap 67 is rather small so that the suspension dwells in the chamber 66 for a relatively long period of time to insure uniform distribution of such suspension all the way around the drive shaft 2. Some suspension flows continuously through the annular gap 67 into the settling space 9 whereby the latter becomes filled to the overflow channel 22. The subsequently admitted suspension displaces solution which escapes by way of the overflow channel 22 and passes through the system of radial channels 23 into the intercepting compartment 24. The flange 68 of the shell 8 compels the inflowing suspension to penetrate well into the settling space 9 and the vanes 13 insure sudden acceleration of inflowing suspension to the speed of the drive shaft 2. The peripheral speed of the outermost portion of the flange 68 corresponds to the speed of such suspension which has entered into the interspaces between the vanes 13 of the shell 8. In order to reach the overflow channel 22, the suspension must reduce its speed during travel radially inwardly toward the axis of the drive shaft 2 (i.e., in the interspaces between the vanes 13). This results in very rapid and highly satisfactory segregation of solid particles. Such solid particles bear against the surfaces of the vanes 13 and the centrifugal force compels them to travel radially outwardly, i.e., counter to the direction of liquid flow toward the overflow channel 22. The solid particles accumulate in the radially outermost part of the settling space 9 whereas the liquid phase is forced to flow radially'inwardly and to leave the settling space by way of the overflow channel 22.

The outermost part of the settling space 9 becomes progressively filled with solid particles which form a cake wherein the particles are closely adjacent to each other. The particles of the cake support and prop each other and bear against each other with a force which depends from their mass, their electrical charge and the rotational speed of the drive shaft 2. Finally, the suspension which enters the settling space 9 reaches the piston 14. A reduction in the depth of sedimentation can, under circumstances, interfere with complete calming down of suspension in interspaces between the vanes 13. The remaining turbulence causes some solid particles to float in the suspension so that the centrifuge runs turbid or muddy." Some of the liquid entering the intercepting chamber 24 of the housing 1 is permanently withdrawn and is caused to flow through a test tube of glass or the like. A conventional photosensitive detector scans the liquid in the test tube and generates a signal when the turbidity of liquid reaches a predetermined value. Such signal is utilized to automatically terminate admission of suspension into the feeding pipe 20 and to close the flow regulating valve 29 in the conduit 30. The control liquid is then caused to leave the annular compartment 43 below the sealing ring 42 and the control chambers 17 below the gasket 18 and ring 19 by way of the orifices 45 (FIG. 3a) under the action of centrifugal force. Thus, the pressure on the piston 14 is reduced so that the piston 14 is retracted back into the groove 17, partly under the bias of the gasket 18 and ring 19 and partly under the pressure of solution in the settling space 9. This opens the ring-shaped outflow passage 44 whereby a conical ring-shaped channel (FIG. 3) develops between the cover 6 and shell 8. Thus, the solution which remained in the settling space 9 can rapidly leave this space radially inwardly of the caked solid particles by way of the channels 44, 85 to enter the system of radial channels 23 and the intercepting compartment 24. The settling space 9 then contains only the cake of solid particles with some liquid entrapped in the capillaries of the cake.

In the meantime, the control liquid has escaped from the annular compartment 43 so that the sealing ring 42 is not subjected to liquid pressure and it ceases to seal the clearance 60. The clearance 60 is located at the lowermost point of the radially outermost portion of the space 9 so that liquid which is entrapped between the solid particles of the cake can escape along the sealing ring 42, through the clearance 60, the connecting bore or channel 69, radial channels 23, and into the intercepting compartment 24. The sealing ring 57 continues to remain in sealing engagement with the end face 7 of the cover 6.

When the filtering step including expulsion of liquid from the cake in the settling space 9 is completed, the flow regulating valve 27 is closed so that the control liquid leaves the channels 49 of the cylinder chamber 11A by way of the gaps between the sections of the piston ring 12. This reduces the pressure in the chamber 11A so that the pressure of the cake in the outermost part of the settling space 9 prevails and causes the shell 8 to move downwardly toward the open position shown in FIG. 3. Thus, the cover 6 then defines with the shell 8 a relatively wide annular discharge opening 61.

Automatic expulsion of the extremely hard and compact cake from the outermost part of the settling chamber 9 is due to a phenomenon which is similar to that observable on detonation of an explosive charge. The cake in the space 9 is capable of standing very high compressive stresses; however, it can stand relatively small bending and tensional stresses. Thus, when the cake is subjected to tangential stresses subsequent to movement of the shell 8 to the open position of FIG. 3, i.e., while the bowl rotates subsequent to such movement of the shell 8, the cake is torn apart; it actually explodes" into a large number of small fragments which are propelled tangentially into the collecting chamber 52 of the housing 1. Since the cake is an anisotropic body, one would expect that lack of uniform strength in all zones thereof would result in the formation of larger and smaller fragments during disintegration and subsequent ejection of particles into the chamber 52, i.e., that the breaking up of the cake into smaller parts would take place at timely spaced intervals. This could result in damage to the centrifuge because the balance of the bowl would be destroyed if certain portions of the cake were permitted to leave the settling space 9 ahead of the others. Improper balance of the bowl would be particularly dangerous at high operating speeds which are desirable in the improved centrifuge to insure satisfactory expulsion of the liquid fraction. It is further desirable to effect expulsion of the cake while the bowl spins at normal operating speed. It was found that such high speed actually assists rapid and trouble-free evacuation of the cake. This is attributed to the fact that the large tangential forces (analogous to radial forces developing on detonation of an explosive charge) compensate for eventual differences in the strength of various sections of the cake. Such tangential forces can readily overcome cohesion between the moist particles of the cake and bring about an "explosion of settled solid material as soon as the barrier (shell 8) which interferes with radial expansion of the cake is removed. It can be said that, as soon as the shell 8 moves to the open position of FIG. 3, the cake of settled particles in the space 9 behaves not unlike a body of liquid and disintegrates during radial expansion so that the chamber 52 receives a mass of finely comminuted solid material. As a matter of fact, the tendency of the cake to expand assists the movement of the shell 8 toward open position as soon as the pressure of control liquid in the cylinder chamber 11A decreases to a certain value.

The mass of comminuted material is expelled from the chamber 52 by the gaseous fluid which is admitted into the space 50 and is accelerated by the surface 51 of the cover 6.

The flow regulating valve 27 is preferably closed in automatic response to movement of the shell 8 to open position so that the shell returns to closed position and the centrifuge is ready to receive a fresh batch of suspension. Such suspension is then treated in a manner as described above. Thus, the treatment of successive batches can be initiated and/or terminated in a fully automatic way.

It will be seen that the treatment of a batch of suspension involves several important steps, namely, sedimentation of solid particles in a closed bowl to accumulate a cake of densely compacted solid particles, filtration of the cake to expel therefrom at least some of the remaining liquid fraction (by way of the clearance 60 and bore 69), and disintegration and simultaneous expulsion of the cake from the settling space 9 whereby the tendency of the cake to expand effects or assists the opening of the bowl. Closing of the bowl is effected by employing a supply of circulating control liquid.

Since the improved centrifuge employs a control liquid, the opening and closing of the bowl is not dependent on the presence or absence of suspension and/or clarified liquid fraction. Furthermore, and since the separated liquid fraction is admitted into a space (compartment 24) which is not intended to receive the solid particles (they are admitted into the collecting chamber 52), the sealing device including the ring 57 can remain in operative position while the bowl rotates to expel liquid from the cake of solid particles (by way of the clearance 60 and connecting bore 69). The provision of a closed circuit for the control liquid constitutes another advantageous feature of the improved centrifuge, i.e., such liquid is available at all times to facilitate opening or closing of the bowl, either automatically or manually, at any desired stage of the operation. The operation of the centrifuge is independent of the specific weight of the liquid fraction, from the presence or absence of suspension in the settling chamber 9, from the difference between the diameters of ring-shaped bodies of suspension, liquid fraction and control liquid which circulate in the apparatus, from the specific weight of the control liquid, and certain other factors.

Another advantage of my centrifuge is that the control liquid is admitted by way of the drive shaft 2. Since the suspension is also preferably. admitted through the shaft, the illustrated centrifuge has been designed to admit suspension by way of one (upper) end and to admit the control liquid by way of the other (lower) end of the drive shaft.

The improved centrifuge is particularly suited for treatment of suspensions which contain extremely small solid particles. The smaller the size of solid particles, the greater are the problems which arise in connection with their separation from a liquid fraction. The length of time required for separation is inversely proportional to the size of solid particles. The same applies for the time which is required for filtration of liquid from accumulated solid particles in the bowl because the size of capillaries between accumulated particles is smaller if the size of particles is smaller. This results in a greatly increased throttling or flow restricting effect of accumulated particles, i.e., it takes longer to expel liquid from a cake which consists of minute solid particles. Very small particles of a suspension form a Newtonian liquid and accumulate into a viscous mass in response to rotation of the bowl.

The problem of segregation of solid particles is particularly acute when the suspension contains a mass of colloidal particles with a size below 0.001 millimeter and if the electric charge of all such particles is the same. Thus, the equally charged particles repel each other and, in the case of simple sedimentation, submerge in the liquid carrier only to the extent of remaining at a predetermined distance from each other, namely, at a distance which is a multiple of the size of a particle. The radial forces to which the particles are subjected in the closed bowl balance the forces which tend to repel the particles from each other, i.e., there develops an equilibrium of forces while the particles remain separated from each other. In order to insure dense packing of the thus charged particles, the radial forces must be raised to an unattainable magnitude because the forces which tend to repel the particles from each other increase with decreasing distance between the particles. The presence of a current-conducting liquid in the interspaces between the particles merely enhances the repelling action. This is the cause for development of the aforementioned turbulent zone which contains a certain percentage of unsettled particles. Were the contents of the turbulent zone evacuated only by way of the clearance 60. such evacuation would take too much time because it would have to penetrate through a body of densely packed solid particles. The densely packed particles accumulate radially inwardly of the clearance 60. Since the control valve 14 is placed inwardly of the clearance 60, but still at a substantial distance from the shaft 2, the contents of the turbulent zone can be evacuated not only rapidly but also in such a way that the liquid need not penetrate through the cake.

The sealing ring 42 of the shell 8 can be replaced with a sealing ring of the type shown in FIGS. 6 and 7. The latter Figures show a deformable ringshaped diaphragm 71 having a ring-shaped bead 72 which is clamped against the adjoining portion of the shell 8 by a clamping ring 70. The lower end face of the clamping ring 70 is formed with a ring-shaped channel 73 which communicates with a channel 36' (corresponding to the channel 36 of FIG. 3). The channel 73 further communicates with a channel 38 (corresponding to the channel 38). The diaphragm 71 defines with the clamping ring 70 a ring-shaped chamber 75 which is adjacent to the underside of the cover 6'. The chamber 75 communicates with the channel 73 by way of one or more bores 74 machined into the clamping ring 70. When the channel 36' admits control liquid to the chamber 75 by way of the channel 73 and the bore or bores 74, the liquid in the chamber 75 deforms the diaphragm 71 so that the latter bears against the cover 6 and seals the clearance 60'. Thus, the connecting bore 69 is then sealed from the settling space 9. If the control liquid is permitted to escape from the chamber 75 by centrifugal force, the diaphragm 71 collapses under the action of centrifugal force (see FIG. 7) to reduce the volume of the chamber 75 and to thus permit liquid to flow from the settling space 9, through the clearance 60 and into the bore 69, as well as into the opening 61 above the sealing ring 57.

FIG. 8 illustrates a portion of a further centrifuge wherein the sealing ring 42 of FIGS. 2 and 3 is replaced with a metallic diaphragm 76. This diaphragm has a thin-walled readily flexible portion or wall 77 the outer side of which is provided with a ring-shaped protuberance or ridge 80 adapted to bear against the adjacent surface of the cover 6. The diaphragm 76 is further provided with an internal chamber 78 and with one or more bores 79 serving to connect the chamber 78 with a ring-shaped channel 73" in the bottom surface of the diaphragm. The channel 73" communicates with the channels 36", 38" ofthe shell 8".

When the channel 36" admits control liquid by way of the channel 73" and bore 79, the liquid fills the chamber 78 and bears against the underside of the wall 77 which is flexed outwardly and presses the ridge 80 against the cover 6" to seal the clearance 60". When the liquid is free to escape from the chamber 78, the wall 77 moves the ridge 80 away from sealing engagement with the cover 6". It will be noted that the diaphragm 76 is weakened, as at 81 and 81a, to enhance the flexibility of the wall 77. The upstanding walls 84, 84a of the diaphragm 76 are relatively stiff to insure that the diaphragm does not undergo excessive deformation in response to admission of control liquid into the chamber 78.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In a centrifuge for treatment of suspensions of solid particles in a liquid fraction, a combination comprising a drive shaft; a bowl driven by said shaft and including a first portion and a second portion movable axially of said shaft to and from a closed position in which said portions define an annular settling space having an outermost part and a narrow clearance outwardly adjacent to said outermost part; first sealing means mounted in said bowl adjacent to said clearance; hydraulic operating means including a supply of control liquid for effecting movements of said sealing means between sealing and open positions; feeding means for supplying batches of suspension into said space in sealing position of said sealing means so that the solid particles accumulate in said outermost part to form a cake containing some of the liquid fraction which is expelled by way of said clearance upon opening of said sealing means; and second sealing means provided between said portions outwardly of said clearance to establish a fluidtight seal in closed position of said second portion.

2. A combination as defined in claim 1, further comprising means defining an intercepting chamber for the liquid fraction, said bowl having channel means for conveying the liquid fraction from said clearance to said intercepting chamber.

3. A combination as defined in claim 1, wherein said first sealing means comprises a ring-shaped elastic sealing member axially movably mounted in one of said portions, said one portion having an annular compartment adapted to receive control liquid and to thereby effect movement of said sealing member across said clearance and into engagement with the other portion of said bowl, said shaft having a passage for admission of control liquid from said operating means to said compartment.

4. A combination as defined in claim 3, further comprising a housing defining with said shaft, said bowl and said operating means a closed circuit for circulation of the control liquid.

5. A combination as defined in claim 1, wherein at least one of said sealing means is provided in the second portion of said bowl.

6. A combination as defined in claim 1, wherein said bowl further comprises a third portion and wherein said second portion is disposed between said first and third portions and defines with said third portion a cylinder chamber, said operating means including means for admitting control liquid into said cylinder chamber to thereby effect movement of said second portion to closed position.

7. A combination as defined in claim 1, wherein one of said portions is provided with an outflow passage communicating with said settling space radially inwardly of said outermost part, said bowl further comprising control valve means for normally sealing said outflow passage and said operating means comprising regulating means for effecting opening of said valve means to thus permit escape of suspension and liquid fraction from the settling space in closed position of said second portion.

8. A combination as defined in claim 7, wherein said outlet passage is provided in said second portion and said second portion is further provided with a ring-shaped groove movably receiving said valve means, a portion of said groove constituting at least one control chamber connected with said operating means by way of a passage provided in said shaft, said valve means sealing said outflow passage when said regulating means admits control liquid to said control chamber.

9. A combination as defined in claim 8, wherein said bowl further comprises stop means for limiting the extent of movement of said valve means with reference to said second portron.

10. A combination as defined in claim 8, wherein said second portion has a surface bounding a portion of said settling space and said valve means has a surface which is flush with the surface of said second portion when said control chamber is filled with control liquid and which is withdrawn into said groove in response to evacuation of control liquid from said control chamber.

11. A combination as defined in claim 8, wherein said valve means comprises an elastic gasket which seals said outlet passage in response to admission of control liquid into said control chamber.

12. A combination as defined in claim 8, wherein said valve means comprises a ring-shaped piston and an elastic ring connecting said piston with said second portion.

13. A combination as defined in claim 1, further comprising means defining an intercepting compartment for the liquid fraction, said bowl having an overflow channel communicating with said settling space radially inwardly of said outermost part and substantially radial channel means for conveying the liquid fraction from said overflow channel into said intercepting compartment.

14. A combination as defined in claim 13, wherein said bowl is further provided with an overflow passage connecting said radial channel means with said settling space at a point located radially outwardly of said overflow channel and valve means controlled by said operating means for normally sealing said overflow passage.

15. A combination as defined in claim 13, wherein said bowl is further provided with additional channel means connecting said clearance with said radial channel means.

16. A combination as defined in claim 1, wherein said bowl is further provided with an overflow passage communicating with said settling space radially inwardly of said outermost part and further comprising valve means installed in said bowl for normally sealing said overflow passage, said bowl defining a compartment adjacent to said first sealing means and at least one control chamber adjacent to said valve means, said shaft and said bowl being provided with passages and channels for admission of control liquid from said operating means to said chamber and said compartment to thereby maintain said first sealing means and said valve means in sealing positions.

17. A combination as defined in claim 1, wherein said how] further comprises a plurality of substantially radially extending vanes in said settling space.

18. A combination as defined in claim 1, wherein said feeding means includes a portion of said shaft, said portion of said shaft having an axial bore for reception of suspension and a plurality of ports for conveying suspension from said bore and away from the axis of said shaft to direct the outflowing suspension backwards.

19. A combination as defined in claim 1, wherein said shaft is vertical and said second portion is located below the first portion of said bowl, said second portion comprising a plurality of substantially radial closely adjacent vanes extending into said settling space and a flange overlapping portions of said vanes.

20. A combination as defined in claim 19, wherein said flange is a ring surrounding those portions of said vanes which are nearer to said shaft.

21. A combination as defined in claim 19, wherein said flange and the first portion of said bowl define a ring-shaped gap for admission of suspension into said settling space.

22. A combination as defined in claim 21, wherein said how] is provided with a ring-shaped distributing chamber located above and communicating with said gap, said feeding means being arranged to admit the suspension to said distributing chamber.

23. A combination as defined in claim 22, wherein said distributing chamber diverges toward said gap and said feeding means includes a portion of said shaft, said portion of said shaft having a plurality of ports for admission of suspension into said distributing chamber.

24. A combination as defined in claim 1, wherein said portions of the bowl comprise ring-shaped metallic end faces located radially outwardly of said outermost part and wherein 7 said second sealing means is arranged to establish a fluidtight seal between said end faces.

25. A combination as defined in claim 24, wherein said second sealing means comprises a deformable sealing ring recessed into one of said end faces and a ring-shaped protuberance provided on the other end face and bearing against said sealing ring in closed position of said second portion.

26. A combination as defined in claim 25, wherein said sealing ring consists of at least substantiall incompressible elastic material and wherein said other end ace [5 provided with at least one groove adjacent to said protuberance to receive elastic material which spills into such groove in response to penetration of said protuberance into said sealing ring.

27. A combination as defined in claim 25, wherein said end faces define a relatively wide ring-shaped discharge opening for evacuation of solid particles from said settling space in response to movement of said second portion away from closed position.

28. A combination as defined in claim 27, wherein said portions include parts which constrict a portion of said discharge opening so that solid particles leaving the settling space by way of said opening bypass said sealing ring and said protuberance.

29. A combination as defined in claim 24, wherein said end faces define a relatively wide discharge opening for evacuation of solid particles from the outermost part of said settling space in response to movement of said second portion away from closed position, and further comprising a housing defining a collecting chamber for reception of solid particles which leave the settling space by way of said opening in response to continued rotation of said bowl, and pneumatic means for expelling solid particles from said collecting chamber.

30. A combination as defined in claim 1, wherein said first sealing means comprises a deformable annular diaphragm mounted in one of said portions and defining therewith a ringshaped chamber adapted to receive control liquid from said operating means to thereby move across said clearance and into sealing engagement with the other portion of said bowl.

31. A combination as defined in claim 30, wherein said diaphragm comprises a bead and said one portion includes a clamping ring which engages said bead and bounds a portion of said chamber.

32. A combination as defined in claim 30, wherein said diaphragm is inwardly adjacent to said chamber and is deformed in response to centrifugal force thereby reduce the volume of said chamber and to thus permit evacuation of liquid fraction by way of said clearance in response to evacuation of control liquid from said chamber.

33. A combination as defined in claim 1, wherein said first sealing means comprises a hollow metallic diaphragm mounted in one of said portions and having a deformable wall adjacent to said clearance and an internal chamber arranged to receive control liquid from said operating means whereby the thus admitted liquid bears against and deforms said wall under the action of centrifugal force to move the wall across said clearance and into sealing engagement with the other portion of said bowl.

34. A combination as defined in claim 1, wherein said bowl further comprises a third portion fixed to said shaft, said second portion being located between said first and third portions and defining with said third portion a cylinder chamber arranged to receive control liquid from said operating means to thereby effect movement of said second portion to closed position, said second and third portions having a plurality of substantially radially extending projections subdividing at least a portion of said cylinder chamber into a plurality of radially extending channels in which the control liquid is accelerated to the speed of said shaft.

35. A combination as defined in claim 1, wherein said shaft is substantially vertical and said feeding means includes the upper end portion of said shaft, said operating means being arranged to admit to said bowl control liquid by way of the lower end portion of said shaft.

M1077 n-r-n 

1. In a centrifuge for treatment of suspensions of solid particles in a liquid fraction, a combination comprising a drive shaft; a bowl driven by said shaft and including a first portion and a second portion movable axially of said shaft to and from a closed position in which said portions define an annular settling space having an outermost part and a narrow clearance outwardly adjacent to said outermost part; first sealing means mounted in said bowl adjacent to said clearance; hydraulic operating means including a supply of control liquid for effecting movements of said sealing means between sealing and open positions; feeding means for supplying batches of suspension into said space in sealing position of said sealing means so that the solid particles accumulate in said outermost part to form a cake containing some of the liquid fraction which is expelled by way of said clearance upon opening of said sealing means; and second sealing means provided between said portions outwardly of said clearance to establish a fluidtight seal in closed position of said second portion.
 2. A combination as defined in claim 1, further comprising means defining an intercepting chamber for the liquid fraction, said bowl having channel means for conveying the liquid fraction from said clearance to said intercepting chamber.
 3. A combination as defined in claim 1, wherein said first sealing means comprises a ring-shaped elastic sealing member axially movably mounted in one of said portions, said one portion having an annular compartment adapted to receive control liquid and to thereby effect movement of said sealing member across said clearance and into engagement with the other portion of said bowl, said shaft having a passage for admission of control liquid from said operating means to said compartment.
 4. A combination as defined in claim 3, further comprising a housing defining with said shaft, said bowl and said operating means a closed circuit for circulation of the control liquid.
 5. A combination as defined in claim 1, wherein at least one of said sealing means is provided in the second portion of said bowl.
 6. A combination as defined in claim 1, wherein said bowl further comprises a third portion and wherein said second portion is disposed between said first and third portions and defines with said third portion a cylinder chamber, said operating means including means for admitting control liquid into said cylinder chamber to thereby effect movement of said second portion to closeD position.
 7. A combination as defined in claim 1, wherein one of said portions is provided with an outflow passage communicating with said settling space radially inwardly of said outermost part, said bowl further comprising control valve means for normally sealing said outflow passage and said operating means comprising regulating means for effecting opening of said valve means to thus permit escape of suspension and liquid fraction from the settling space in closed position of said second portion.
 8. A combination as defined in claim 7, wherein said outlet passage is provided in said second portion and said second portion is further provided with a ring-shaped groove movably receiving said valve means, a portion of said groove constituting at least one control chamber connected with said operating means by way of a passage provided in said shaft, said valve means sealing said outflow passage when said regulating means admits control liquid to said control chamber.
 9. A combination as defined in claim 8, wherein said bowl further comprises stop means for limiting the extent of movement of said valve means with reference to said second portion.
 10. A combination as defined in claim 8, wherein said second portion has a surface bounding a portion of said settling space and said valve means has a surface which is flush with the surface of said second portion when said control chamber is filled with control liquid and which is withdrawn into said groove in response to evacuation of control liquid from said control chamber.
 11. A combination as defined in claim 8, wherein said valve means comprises an elastic gasket which seals said outlet passage in response to admission of control liquid into said control chamber.
 12. A combination as defined in claim 8, wherein said valve means comprises a ring-shaped piston and an elastic ring connecting said piston with said second portion.
 13. A combination as defined in claim 1, further comprising means defining an intercepting compartment for the liquid fraction, said bowl having an overflow channel communicating with said settling space radially inwardly of said outermost part and substantially radial channel means for conveying the liquid fraction from said overflow channel into said intercepting compartment.
 14. A combination as defined in claim 13, wherein said bowl is further provided with an overflow passage connecting said radial channel means with said settling space at a point located radially outwardly of said overflow channel and valve means controlled by said operating means for normally sealing said overflow passage.
 15. A combination as defined in claim 13, wherein said bowl is further provided with additional channel means connecting said clearance with said radial channel means.
 16. A combination as defined in claim 1, wherein said bowl is further provided with an overflow passage communicating with said settling space radially inwardly of said outermost part and further comprising valve means installed in said bowl for normally sealing said overflow passage, said bowl defining a compartment adjacent to said first sealing means and at least one control chamber adjacent to said valve means, said shaft and said bowl being provided with passages and channels for admission of control liquid from said operating means to said chamber and said compartment to thereby maintain said first sealing means and said valve means in sealing positions.
 17. A combination as defined in claim 1, wherein said bowl further comprises a plurality of substantially radially extending vanes in said settling space.
 18. A combination as defined in claim 1, wherein said feeding means includes a portion of said shaft, said portion of said shaft having an axial bore for reception of suspension and a plurality of ports for conveying suspension from said bore and away from the axis of said shaft to direct the outflowing suspension backwards.
 19. A combination as defined in claim 1, whereiN said shaft is vertical and said second portion is located below the first portion of said bowl, said second portion comprising a plurality of substantially radial closely adjacent vanes extending into said settling space and a flange overlapping portions of said vanes.
 20. A combination as defined in claim 19, wherein said flange is a ring surrounding those portions of said vanes which are nearer to said shaft.
 21. A combination as defined in claim 19, wherein said flange and the first portion of said bowl define a ring-shaped gap for admission of suspension into said settling space.
 22. A combination as defined in claim 21, wherein said bowl is provided with a ring-shaped distributing chamber located above and communicating with said gap, said feeding means being arranged to admit the suspension to said distributing chamber.
 23. A combination as defined in claim 22, wherein said distributing chamber diverges toward said gap and said feeding means includes a portion of said shaft, said portion of said shaft having a plurality of ports for admission of suspension into said distributing chamber.
 24. A combination as defined in claim 1, wherein said portions of the bowl comprise ring-shaped metallic end faces located radially outwardly of said outermost part and wherein said second sealing means is arranged to establish a fluidtight seal between said end faces.
 25. A combination as defined in claim 24, wherein said second sealing means comprises a deformable sealing ring recessed into one of said end faces and a ring-shaped protuberance provided on the other end face and bearing against said sealing ring in closed position of said second portion.
 26. A combination as defined in claim 25, wherein said sealing ring consists of at least substantially incompressible elastic material and wherein said other end face is provided with at least one groove adjacent to said protuberance to receive elastic material which spills into such groove in response to penetration of said protuberance into said sealing ring.
 27. A combination as defined in claim 25, wherein said end faces define a relatively wide ring-shaped discharge opening for evacuation of solid particles from said settling space in response to movement of said second portion away from closed position.
 28. A combination as defined in claim 27, wherein said portions include parts which constrict a portion of said discharge opening so that solid particles leaving the settling space by way of said opening bypass said sealing ring and said protuberance.
 29. A combination as defined in claim 24, wherein said end faces define a relatively wide discharge opening for evacuation of solid particles from the outermost part of said settling space in response to movement of said second portion away from closed position, and further comprising a housing defining a collecting chamber for reception of solid particles which leave the settling space by way of said opening in response to continued rotation of said bowl, and pneumatic means for expelling solid particles from said collecting chamber.
 30. A combination as defined in claim 1, wherein said first sealing means comprises a deformable annular diaphragm mounted in one of said portions and defining therewith a ring-shaped chamber adapted to receive control liquid from said operating means to thereby move across said clearance and into sealing engagement with the other portion of said bowl.
 31. A combination as defined in claim 30, wherein said diaphragm comprises a bead and said one portion includes a clamping ring which engages said bead and bounds a portion of said chamber.
 32. A combination as defined in claim 30, wherein said diaphragm is inwardly adjacent to said chamber and is deformed in response to centrifugal force thereby reduce the volume of said chamber and to thus permit evacuation of liquid fraction by way of said clearance in response to evacuation of control liquid from said chamber.
 33. A combination as defined in claim 1, wherein said first sealing means comprises a hollow metallic diaphragm mounted in one of said portions and having a deformable wall adjacent to said clearance and an internal chamber arranged to receive control liquid from said operating means whereby the thus admitted liquid bears against and deforms said wall under the action of centrifugal force to move the wall across said clearance and into sealing engagement with the other portion of said bowl.
 34. A combination as defined in claim 1, wherein said bowl further comprises a third portion fixed to said shaft, said second portion being located between said first and third portions and defining with said third portion a cylinder chamber arranged to receive control liquid from said operating means to thereby effect movement of said second portion to closed position, said second and third portions having a plurality of substantially radially extending projections subdividing at least a portion of said cylinder chamber into a plurality of radially extending channels in which the control liquid is accelerated to the speed of said shaft.
 35. A combination as defined in claim 1, wherein said shaft is substantially vertical and said feeding means includes the upper end portion of said shaft, said operating means being arranged to admit to said bowl control liquid by way of the lower end portion of said shaft. 